Undulator Specifications Undulator Overview FEL Performance Assessment Recent Undulator Parameter Changes
advertisement
Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL November 14, 2003 Undulator Overview FEL Performance Assessment Recent Undulator Parameter Changes Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac Coherent Light Source Near Hall Undulator Far Hall Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Undulator Schematic (Regular Section) 3,410 406 863 mm UNDULATOR 11,905 mm Horizontal Steering Coil Total Length 130,092 mm Vertical Steering Coil Beam Position Monitor X-Ray Diagnostics Quadrupoles Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center SASE FELs SASE FEL theory well developed and verified by simulations FEL radiation starts from noise in spontaneous radiation Saturation Exponential Gain Regime Undulator Regime Transverse radiation electric field modulates the energy and bunches the electrons within an optical wavelength 1 % of X-Ray Pulse Exponential build-up of radiation Electron Bunch along undulator length Micro-Bunching Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Expected Performance Start-To-End Simulations: Parmela Elegant Genesis / Ginger space-charge compression, wakes, CSR, … SASE FEL with wakes Low charge cases are modeled in PARMELA after the GTF results and then imported into ELEGANT/GENESIS for the transport through the LCLS beam line. The simulations includes: Space charge in the gun Emittance compensation Wakefield and CSR effects Optimized beam transport (Jitter) Spontaneous Undulator Radiation All cases reach saturation Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Workshop on Start-To-End Simulations Beam Dynamics Mini Workshop Future Light Sources Start-To-End Simulations for SASE FELs (S2E 2003) Chaired by John Galayda (SLAC) and Joerg Rossbach (DESY) Dates August 18 – 22, 2003 Location DESY-Zeuthen, Berlin, Germany Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Comparison of GINGER/GENESIS results for 1-nC LCLS “0-order” Case Observations: • GENESIS shows very slightly longer gain length, later saturation but higher power • GINGER shows stronger post-saturation power oscillation (more deeply trapped particles?) • Method for choosing best K was slightly different for both codes Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center GINGER/GENESIS results for “0-order” 200-pC case Observations: • Again, GENESIS shows slightly longer gain length, 10-m later saturation but 15% higher power • Again, GINGER shows deeper postsaturation power oscillation • Little sensitivity (2 m, 7%) in GINGER results to 8X particle number increase • Possible reasons for differences: bugs slight differences in initial e-beam properties (e.g. mismatch) grid effects (e.g. outer boundary) ??? Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center 1-nC LCLS: “1st-order” envelope reconstruction: max P(z) vs. slice time 100 GW 100 GW GINGER GENESIS Some quick observations: • Power suppressed in regions with high energy spread [-90:-70 fs] • GENESIS shows ~2-3X greater power than GINGER for no-wake cases • For runs including wake fields, GINGER shows somewhat more peak power for the main body (but more localized in time) • Beam centroid wander may be important – better modeled by GENESIS Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Tolerance Analysis: RON R. Dejus, N. Vinokurov Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Linac Coherent Light Source Undulator Performance Requirements (as of May 2003) 3.6350 Parameter Symbol Target (Nom.) Effective Undulator Parameter K 3.711 Average Gap Height g 6.0 mm +0.006 Average Period Length lu 30.00 mm ±0.03 Wiggle Plane Units 6.5 Tolerance (critical) ±0.015 % horizontal — RMS Trajectory Straightness Tolerance Dx 2 mm — RMS Segment Phase Shake Tolerance Df 10 degrees — Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Trajectory Straightness Requirement Preserve transverse overlap between beam and radiation => Tolerance for betatron amplitude < 8 mm (beam radius dep.) Avoid longitudinal phase shake between beam and radiation => Tolerance for rms phase shake 10 degrees per module => Equivalent tolerance for rms electron beam straightness 2 mm Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Workshop on Undulator Parameters LCLS Undulator Parameter Workshop Chaired by Heinz-Dieter Nuhn (SLAC) Dates November 24, 2003 Location APS, Argonne, USA Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Workshop Focus Set Undulator Period Reduction of maximum available linac energy Undulator gap height increase Longer break distances Weaker FODO lattice Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Adjusting Estimate of On-Axis Undulator Field Halbach formula for hybrid undulator is used to estimate relation between gap/period and on-axis field Bae gap gap b c period period 2 a 3.44 T b 5.08 c 1.54 period 3 cm B 1.325 T gap 6.00 mm Measured prototype field 5.3% larger than estimated a 3.62 T b 5.08 c 1.54 Undulator Parameter Workshop, November 14, 2003 Undulator Specifications period 3 cm B 1.325 T gap 6.35 mm Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Undulator Period Present undulator period length of 3 cm is near optimum for shortest gain length Change of undulator period length would require more man-power and time than available before next review Undulator period length will be kept at lu = 3.0 cm Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Maximum Available Linac Energy 14.35 GeV has been nominal energy to reach 1.5 Å Loss of available linac energy due to Reduction of available linac sections (incl. Injector relocation) Off-crest acceleration New maximum energy set to 14.1 GeV to restore operational overhead Requires change in K value Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Undulator Gap Selection Undulator gap height changes still possible Present gap height: 6 mm Gap height corrected for measured field: 6.35 mm Parameter correction for reduced maximum energy gap 6.5 mm Bmax 1.298 T K 3.6350 More Room for Vacuum Chamber E 14.09 GeV lr 1.5 Å E 4.46 GeV lr 15.0 Å New Parameters Larger gap gives access to short wavelength 1.0 Å gap 8.2 mm Bmax 1.013 T K 2.838 Undulator Parameter Workshop, November 14, 2003 Undulator Specifications E 14.03 GeV lr 1.0 Å E 11.46 GeV lr 1.5 Å E 3.62 GeV lr 15.0 Å Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Undulator Large Gap / Low K Proposal Based on Chosen Parameters Proposed Undulator Length Safety Overhead Emittance Goal Emittance Achieved Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center New Break Lengths Separations between undulator modules (breaks) designed to produce slippage by integer number of optical wavelength. Break increments for adding slippage of 1 optical wavelength is DLB=lu (1+K2/2). DLB=23.7 cm (old); 22.8 cm (new) Present design uses break pattern 1-1-2 which corresponds to the lengths sequence 18.7 cm – 18.7 cm – 42.1 cm 18.7 cm gives not enough space for quads, BPMs, etc. Length needed > 30 cm 42.1 cm gives not enough space for x-ray diagnostics Length needed > 70 cm New break pattern 2-2-4 corresponding to length sequence 40.6 cm – 40.6 cm – 86.3 cm Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Weaker FODO Lattice FODO Lattice had been designed for <bx,y>=18 m at 1.5 Å Required gradient of 106-107 T/m for 5 cm long quads New gradient set to 60 T/m to Increase Saturation Power Relax Beam-Based Alignment Tolerances Saturation length only slightly increased Average beta function at 1.5 Å is now <bx,y>=30 m Focusing and defocusing magnets will be identical Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Optimum b-Function at Short Wavelength 14.1 GeV Optimum Beta-Function New Beta-Function Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Operating Points for 1 nC Bunch Charge (Old) LCLS Operating Point at 1.5 Å Undulator Parameter Workshop, November 14, 2003 Undulator Specifications LCLS Operating Point at 15 Å Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Operating Points for 1 nC Bunch Charge (New) Operating Point Operating Point LCLS Operating Point at 1.5 Å Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center LCLS Operating Points for 1 nC Bunch Charge (New) Operating Point Operating Point LCLS Operating Point at 15 Å Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Beam Based Alignment Tolerances (Paul Emma) description value unit BPM rms resolution 1 mm BPM offsets (uncorrelated) 50 mm 100 BPM offsets (correlated) 3 00 mm rms BPM ‘random-walk’ over length of undulator BPM mean calibration error 10 % mean calibration error of all BPMs BPM rms calibration spread 3 % rms calibration error spread over BPMs quad. offsets (uncorrelated) 50 mm 100 quad. offsets (correlated) 3 00 mm rms quad ‘random-walk’ over length of undulator quad. mean gradient error 0.3 % mean gradient error of all quadrupoles quad rms gradient error spread 0.3 % rms gradient error spread over quadrupoles undulator rms pole field errors 0.1 0.04 % rms pole field errors spread mover mean calibration error 5 % mean calibration error of all magnet movers mover rms calibration spread 3 % rms calibration error spread over magnet movers mover reproducibility (backlash) 01 mm incoming mean trajectory error 10 initial constant launch error in units of rms beam size incoming rms trajectory jitter 0-0.1 initial variable launch error in units of rms beam size rms energy measurement error 2 % uncertainty in knowledge of beam energy Undulator Parameter Workshop, November 14, 2003 Undulator Specifications comments 2 4 net resolution not necessarily single pulse rms BPM-to-BPM survey and electrical offsets rms quad-to-quad survey errors backlash mover attains setting to within 1 mm Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Summary of Nominal Undulator Design Changes Undulator Type Magnet Material Wiggle Plane Gap Period Length Peak On-Axis Field K OLD planar hybrid NdFeB horizontal 6 3.0 1.325 3.711 NEW planar hybrid NdFeB horizontal 6.5 3.0 1.298 2.635 Module Length Number of Modules Undulator Magnet Length 3.41 33 112.5 3.41 33 112.5 m Break Length Total Device Length 18.7-18.7-42.1 121.8 40.6-40.6-86.3 130.2 cm m Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu mm cm T m Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Summary of Nominal Focusing Lattice Changes Lattice Type Magnet Type Nominal Magnet Length QF Gradient QD Gradient Average b Function at 1.5 Å Lowest Usable Energy Undulator Parameter Workshop, November 14, 2003 Undulator Specifications OLD NEW FODO permanent 5 107 -106 18.0 3.17 FODO permanent 5 60 -60 30 1.84 Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu cm T/m T/m m GeV Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Summary of Electron Beam Parameters At 1.5 Å OLD NEW Electron Beam Energy g <b> rms beam radius 14.35 28082 18.0 36 14.09 27580 30.0 35 At 15 Å OLD NEW Electron Beam Energy g <b> rms beam radius 4.45 8880 7.3 35 4.46 8722 8.9 34 Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu GeV m mm GeV m mm Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center Conclusions Requirements for LCLS undulator are well established LCLS undulator performance requirements are well understood Risks have been assessed and undulator specifications address the risk New parameter values have been chosen Increase in undulator gap, reduction in maximum electron beam energy, longer break length, and reduced quadrupole gradients Benefits are more room for vacuum chamber more energy safety margin more space for diagnostics components between undulator modules increase of accessible wavelength range Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu Linac Coherent Light Source Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center End of Presentation Undulator Parameter Workshop, November 14, 2003 Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL Nuhn@slac.stanford.edu
